An air conditioning apparatus for making connection between the plurality of outdoor units and the plurality of indoor units by refrigerant pipe is widely used conventionally. In such an air conditioning apparatus, a refrigerant flow rate in a refrigerant circuit varies greatly depending on, for example, a difference in the number of rotations of a compressor mounted in each of the outdoor units or the number of operations of the outdoor units. Since a refrigerant oil of the compressor is discharged from the compressor together with a refrigerant and flows through the refrigerant circuit, distribution of the refrigerant oil between the outdoor units may be unbalanced with variations in the refrigerant flow rate.
Known means for solving the above problem is an air conditioning apparatus having an oil equalizing pipe communicating between compressors mounted in different outdoor units as disclosed in, for example, JP-A-2011-226714. In the air conditioning apparatus disclosed in Patent Reference described above, a difference is caused in internal pressure between the compressors by changing the numbers of rotations of the plurality of compressors by a predetermined number of rotations. When the difference is caused in internal pressure between the compressors, a refrigerant oil is moved between the compressors with a pressure difference through the oil equalizing pipe, with the result that unbalance of the amount of refrigerant oil between the compressors, namely, between the outdoor units can be eliminated by sequentially changing the pressure difference between the plurality of compressors.
In the air conditioning apparatus having the plurality of outdoor units, depending on air conditioning capability required by an operated indoor unit, the number of rotations of the compressor of one outdoor unit may be made higher than the number of rotations of the compressor of the other outdoor unit. In such a case, while a large amount of refrigerant oil is discharged from the compressor of the outdoor unit driven at a high number of rotations together with a refrigerant, a small amount of refrigerant oil is discharged from the compressor of the outdoor unit driven at a low number of rotations together with the refrigerant. When such a state continues, a large amount of refrigerant oil may be unbalanced in the outdoor unit with a low number of rotations of the compressor.
In the case of using the oil equalizing pipe described in Patent Reference described above in the air conditioning apparatus as described above, it is necessary to connect the portion between the outdoor units by the oil equalizing pipe. In this case, the number of oil equalizing pipes according to the number of outdoor units installed is required, and there is a problem of increasing cost since the number of oil equalizing pipes is increased as the number of outdoor units installed is increased. Also, when one outdoor unit of the plurality of outdoor units is installed in a place separate from another outdoor unit, the length or the shape of the oil equalizing pipe must be changed according to the installation place of the outdoor unit, and there is a problem of decreasing workability in the case of installing the air conditioning apparatus.